MOSCOW—The Kremlin criticized the U.S. decision to arm Syrian opposition fighters and said Washington's evidence that the Syrian regime is using chemical weapons was unconvincing, but said Friday that Moscow is "not yet" discussing its plans to deliver of air-defense missiles to the regime.

President
Barack Obama
on Thursday authorized the U.S. to arm fighters against the Syrian President
Bashar al-Assad's
regime, reversing a policy of giving only nonlethal support to the country's opposition in the two-year-old civil war. The White House cited confirmation that Mr. Assad's regime had killed up to 150 people with chemical weapons as the reason for its about-face.

Syria in the Spotlight

Track the latest events in a map, see the key players and a chronology of the unrest.

U.K. Prime Minister
David Cameron
said Friday that Britain hadn't yet decided to supply arms to the rebels alongside the U.S., but welcomed Washington's assessment of Syrian weapons use. The U.K. and France were instrumental in ending a European Union arms embargo on Syria, paving the way for increased European assistance to rebel forces.

Mr. Cameron was due to discuss the situation in Syria with Mr. Obama later Friday, a spokesman said. French officials are expected to meet over the weekend with Gen. Salim Idris, who commands the coalition of moderate rebel forces, to discuss future aid including possible arms supplies, according to a French official.

More on Syria

The U.S. move comes ahead of a meeting between Mr. Obama and Russian President
Vladimir Putin
on the sidelines of the G-8 summit in Northern Ireland that starts on Monday. Syria will be at the top of the agenda for the sidelines meeting.

U.N. Secretary-General Ban Ki-moon said Friday that he opposed the U.S. decision to send arms. "There is no such military solution. Only a political solution can address this issue sustainably; therefore, [increasing] the flow of arms to either side would not be helpful," he said.

Mr. Ban also emphasized the need for Syria to allow an on-the-ground investigation to "establish the facts."

If the United States military gets directly involved with the conflict in Syria, what would the objective be? U.S Army Vice Chief of Staff Gen. John Campbell outlines the challenges facing the United States regarding the Syrian civil war.

The Syrian government on Friday dismissed U.S. charges that it used chemical weapons as "full of lies," accusing Mr. Obama of resorting to fabrications to justify his decision to arm Syrian rebels, the AP reported.

Officials from Russia, which along with Iran is Mr. Assad's most prominent foreign ally, said the evidence on chemical weapons isn't rock solid.

"We had a meeting with American representatives in which Americans tried to present information to us about the regime's use of chemical weapons, but frankly speaking, the evidence Americans set out looks unconvincing,"
Yuri Ushakov,
the Kremlin's top foreign-policy aide, said Friday, according to Russian news agencies.

Mr. Ushakov cited the flawed intelligence assessment from the administration of former President George W. Bush about weapons of mass destruction in the run-up to the Iraq war but said he didn't want to "draw any parallels."

Other Russian officials were more direct. "The data on Assad's use of chemical weapons is fabricated just like the lies about weapons of [Saddam] Hussein's weapons of mass destruction," read a tweet on the feed of
Alexei Pushkov,
chairman of the Russian parliament's international relations committee. "Obama is going down the path of G. Bush."

The Kremlin opposes any international action against its longtime client, Mr. Assad.
Russian officials have said they plan to fulfill a 2010 contract for the S-300 missiles as a way to deter potential outside military intervention in the Syrian civil war. Western powers and Israel have opposed the sale of the system.

Both Moscow and the U.S. are pushing the warring sides in Syria to enter peace talks in the coming months.

But opposition forces have appealed for more weapons and support in recent weeks as they've lost ground against Mr. Assad's troops and their allies from the Iranian-backed Lebanese organization Hezbollah.

The U.S. conclusion that Mr. Assad's regime has wielded chemical weapons was based on physical samples taken from Syria, said
Ben Rhodes,
the White House Deputy National Security Adviser for Strategic Communications.

He said the U.S. relied on "multiple, independent streams of information" and has "high confidence" in the assessment. He cited four dates and locations at which the U.S. believes Mr. Assad's regime employed chemical weapons.

Mr. Ushakov, who long served as the Russian ambassador to the U.S., said any extension of the White House's support for Syria's opposition fighters won't help a joint effort by the U.S. and Russia to bring the bloody conflict's opposing sides to the negotiating table.

Russian Ministry of Foreign Affairs spokesman Alexander Lukashevich said the move suggests U.S. efforts to bring the opposition to the peace talks had stalled. He said pumping arms into Syria will increase "the level of armed confrontation and violence against civilians" and reiterated Russia's commitment to a peaceful resolution to the conflict.

U.S. officials have stressed that Mr. Assad, backed by Hezbollah, has been making gains more than two years into a violent conflict that has left more than 93,000 people dead, according to United Nations figures. But before Thursday, the U.S. didn't agree to provide weapons to the opposition, citing concerns that new arms could wind up in the hands of extremists and might not change the balance on the ground, as well as uncertainty about reports of the regime's use of chemical weapons.

ENLARGE

A Free Syrian Army fighter wearing a gas mask carries his weapons as he walks past a damaged tank near Idlib, Syria.
Reuters

Some U.K. lawmakers have voiced similar concerns, complicating any British efforts to arm rebels.

"What is clear today is that…in our world today there is a brutal dictator who is using chemical weapons under our nose in a conflict where almost a 100,000 people have already died—and what is important is that we work with our partners to do what we can to bring this to an end," Mr. Cameron said Friday.

The Syrian regime is a longtime Kremlin ally dating back to the days of the Cold War. Mr. Putin has opposed outside military intervention in the Syrian conflict, and Russia has joined China in vetoing three U.N. resolutions that were aimed at forcing Mr. Assad to step down.

Mr. Ushakov stressed that the U.S. and Russia aren't "competing on Syria," and are trying to find a constructive way to solve the problem in the region.

Syria's government signed a contract in 2010 to buy four S-300 batteries with 144 missiles for $900 million, and the first deliveries were scheduled to start this summer. The weapons could change the power dynamic in the Middle East and help the Assad regime prevent the sort of military campaign Western governments organized to aid rebels fighting Col. Moammar Gadhafi in Libya.

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